The terrorist attacks of Sept. 11, 2001, were originally envisioned as an even more audacious assault involving 10 hijacked jetliners on the East and West coasts, but the plan was scaled back and later plagued by conflicts among al Qaeda's leaders and some of the hijackers themselves, according to a report issued yesterday by the panel investigating the attacks.

The date for the attacks was uncertain until about three weeks before they were carried out, and there is evidence that as late as Sept. 9 ringleader Mohamed Atta had not decided whether one aircraft would target the U.S. Capitol or the White House, according to the report. Atta finally chose a date after the first week of September, the report says, "so that the United States Congress would be in session."

The 20-page document represents the most vivid, detailed and authoritative account of the plot to emerge since the 19 hijackers killed nearly 3,000 people by crashing four jetliners into the World Trade Center, the Pentagon and the Pennsylvania countryside. The document, brimming with new details, features a revealing examination of the thinking and actions of al Qaeda leaders, including Osama bin Laden, and demonstrates how relentlessly the terrorists pursued the plan to its deadly ends.

It also provides the most extensive view so far of what has been learned from secret interrogations of al Qaeda operatives now in U.S. custody, particularly Khalid Sheik Mohammed, mastermind of the attacks, and Ramzi Binalshibh, the would-be hijacker who could not gain entry to the United States and became the coordinator of the plot from Germany.

The narrative portrays bin Laden as a micromanager deeply involved in planning the strikes. He chose all 19 hijackers himself and constantly pushed to move up the attacks, seeking to carry them out as early as the middle of 2000.

Mohammed, the document shows, was the overeager lieutenant who first proposed using airplanes as missiles, but whose grandiose plans were curtailed several times in the face of logistical obstacles. The entire plot, from start to finish, cost al Qaeda only $400,000 to $500,000, the investigation found.

At the same time, the report reveals serious rifts among the hijackers and within the upper ranks of al Qaeda. One of the pilots crucial to the hijack plan, Ziad Samir Jarrah, nearly abandoned the plot and probably would have been replaced by alleged conspirator Zacarias Moussaoui, the only person in the United States charged in connection with the attacks, the report concludes.

But bin Laden's fervor persisted despite opposition from some of his closest aides, who urged him to abandon the plan as it neared completion in the summer of 2001.

Bin Laden believed "that an attack against the United States would reap al Qaeda a recruiting and fundraising bonanza," the report concludes. "In his thinking, the more al Qaeda did, the more support it would gain. Although he faced opposition from many of his most senior advisers . . . bin Laden effectively overruled their objections, and the attacks went forward."

The findings were contained in one of two reports issued yesterday as part of the last round of public hearings held by the National Commission on Terrorist Attacks Upon the United States. The panel, which is to issue a set of conclusions on the nation's air defense system today, is scheduled to complete its wide-ranging final report by next month.

Commission members and witnesses also warned yesterday of the continuing danger posed by al Qaeda, despite the United States' aggressive campaign to thwart it. FBI counterterrorism chief John S. Pistole said that counterterrorism officials have "probably prevented a few aviation attacks" in the United States but that some of the operatives in those plots remain at large.

Al Qaeda "is actively pooling whatever resources it has left at its disposal and, in a very centralized and methodical way, we believe that it is plotting an attack and moving an attack forward using what capabilities it has left to attack the homeland in the next few months," Pistole said.

In their account of the Sept. 11 plot, the panel's staff investigators generally concur with the FBI that there is little evidence that knowing accomplices in the United States aided the plot. The report rules out terrorist connections to a Saudi national who helped two of the hijackers find an apartment in San Diego and found no evidence that the Saudi royal family or government funded the plot. A previous investigation by a joint House-Senate inquiry raised questions about possible complicity by other Saudis besides the 15 hijackers from the desert kingdom.

But the commission raises new questions about a handful of other individuals connected to the hijacking teams, including a man recently deported to Yemen who allegedly bragged to a cellmate about helping two of the hijackers.